Developer for electrophotographic purposes and process for developing an electrostatic image



United States Patent C DEVELGPER FUR ELECTRUPHQTQGRAPHEC PUR- PGSES ANDPRQCES?) FUR DEVELQPFNG AN ELECTROSTATEC IMAGE Martha Torr-ranch, HansEehmenburg, Wilhelm Neugebatter, and Kurt-Walter Klupfel, all ofWieshaden-Biebrich, Germany, assignors, by mesne assignments, toAzoplate Corporatinn, Murray Hill, N3.

N Drawing. Filed June 13, 1960, Ser. No. 35,448 Claims priority,application Germany June 27, 1959 28 Claims. (Cl. 117-175)Electrophotographic material usually consists of a support having alayer of a photoconductive substance. This layer is provided, in theabsence of light, with an electrostatic charge. Then, the material isexposed to light, either through a master or by episcopic projection, animage corresponding to the master thereby being obtained. This image ismade visible by brief contact with a resin powder and, subsequently, itis fixed by heating or by the action of solvents. By thiselectrophotographic procedure, a copy of the master is obtained, whichcannot be wiped off.

The present invention refers to a special kind of developer used forsuch electrophotographic processes.

Usually, the developers are composed of a mixture of a carrier and atoner. The carrier consists of grains of inorganic materials, such astiny glass balls, iron filings, or crystals of inorganic salts, such assodium chloride or potassium chloride.

As toner, resin powders are used which contain dyestuffs or pigments,for example carbon black. When working with the developer, the toner ispositively charged, due to the triboelectric effect between the tonerand the carrier material.

The photoconductive layers can be positively or negatively charged sothat, after exposure beneath a master,

a positive or negative electrostatic image is obtained. An imagecorresponding to the master is formed when the developer, with thepositively charged toner, is applied to a negative electrostatic image.But if the same developer is applied to a positively charged image, thetonal values are reversed; a negative of theoriginal charge image isformed, because the toner particles are repelled by the chargedportions. These reversed images show very little contrast and someundesired marginal eflfects.

As many photoconductive layers can more easily'be charged positivelythan negatively, efiforts were made to find developers with toners whichcan be negatively charged. For this purpose organic carriers, such ascrystals of tanthracene or fluorene were used, or the individualparticles of an inorganic carrier material, such as glass, were coatedwith a resin layer and added to a toner.

By this procedure the toner is charged negatively, but the carriercrystals 13.1'6 of low mechanical strength and pulverize when used in anundesired manner. If inorganic carriers coated with organic material areused, lumps tend to be formed when coating the carrier particles with aresin layer, and, furthermore, the coated carrier particles tend to losetheir round shape which impedes the cascading of the developing powderover the surface of the electrophotographic material. Moreover, theresin coat of the carrier particles is rubbed off, so that the toner isno longer uniformly charged. In some cases, the images obtained usingsuch a toner show an ambiguous electric eflfect, e.g. they appear inpart as images corresponding to the master, in part as reversed images.

Now a developer for electrophotographic purposes has been found,consisting of a carrier and a toner, which can be negatively charged,characterized in that the carrier consists of inorganic materials andthe toner consists at least partially of metal resinates.

Inorganic materials suitable as carriers are: glass, metals, such asiron; and salts, such as potassium sulfate, potassium chloride andsodium chloride. Mixtures of such inorganic carriers can also be used.

In general, the carriers are used in the form of particles having anaverage grain size from about to about 600p. Smaller or larger carrierparticles can also be used, but carriers with a grain size in the rangestated above, preferably from about 100 to about 400 are preferred.Mixtures comprising carriers of different grain sizes can also be used.

Suitable toners are metal resinates, to which pigments and/or dyestuifs,preferably metallic dyestuffs may be added. Metal resinates, :alsocalled resin soaps, are the salts of the metals of Groups l8 of thePeriodic Table with resin acids (s. Rompp, Chemielexikon, 4th edition,page 1858). Preferred metal resina-tes are those of such metals asaluminum, barium, lead, calcium, cerium, iron, cobalt, copper,magnesium, manganese, and zinc. Mixtures of such metal resinates canalso be used.

Resins and/or waxes and/or aromatic organic compounds having a lowmelting point, and substitution products thereof, can also be added.Resins which may be added to the metal resinates are natural resins,such as colophony, dammar resin, copals, e.g. Manila copal or kauricopal, and synthetic resins, such as ketone resins, maleic resins, alkydresins, and styrene resins.

Waxes used for this purpose are natural waxes, such as carnauba wax,beeswax, Japan wax, montan wax, and synthetic waxes, such as the onescommercially available as A wax, OP wax, SPO wax, V wax, and especiallythe so-c-alled Gersthofener Wachse, marked as KP, S, L, and 0.

As low melting aromatic compounds there may be added unsubstituted andsubstituted compounds having melting points in the range of about 40 toabout C. Such aromatic organic compounds are naphthols, such asl-naphthol or Z-naphthol, acenaphthene, o-phenylene diamine, resorcinol,and diphenylamine. These materials are added for the purpose of reducingthe melting point of the toner mixture and increasing the adhesionthereof.

The metal resinates may be colored; for this purpose, pigments are used,such as carbon black, zinc oxide, titanium dioxide, ul-tramarine,minium, pigment red B, and pigment green B. Generally, however, not morethan 10 percent of pigments should be added in order to limit theinfluence on the charging characteristics.

Moreover, dyestuffs can be added, which contain metal elements. In thiscase, larger quantities can be used, for example 50 percent, butpreferably 35 percent should not be exceeded.

Dyestuffs with a metal content are e.g. complex compounds containing intheir molecules copper, zinc, magnesium, iron, sodium or potassium, viz.chlorophyll or copper-, zincor magnesium-phthalocyanine or naphtholgreen 5. Further double salts of dyestuff molecules, for instance, thezinc double salt of toluidine blue 0, methylene green B, or acridineorange 26, are used.

Complex salts of heteropoly acids, such as phosphortungstomolybdic acidwith dyestuffs may also be used, e.g. the so-called fanal dyestufis, forinstance Fanal Red 613, Fanal Violet LB, and Fanal Blue B. Furthermore,metal salts of sulfonic or carboxylic acids of dyestuffs may be used,for instance Alizarin blue'olack B, and Diamant Black F. For coloringthe metal resinates dyestuffs may also be used which contain no metalliccomponents, e.g. Nigrosin, Pigment Deep Black, Auramin, BrilliantYellow, Eosin, Rhodamine B,

and Sudan Black G. Moreover, mixtures of the above ditferent kinds ofdyestutfs can be used.

For the preparation of the toner, the crushed initial materials areadvantageously mixed and then finely ground, for example in a ball mill.Then, the mixture is melted, and the molten mass is thoroughly mixed, toembed the coloring particles completely in the resin. In-

sofar as they are fusible, the initial products can be melted The abovedeveloper may be used in known electrophotographic procedures.

developer powder that, when used in the method described in Example 1,forms negative images of the originals used.

Example 3 The method described in Example 1 is repeated, meltingtogether parts by weight of a calcium resinate (KunstharzL), 30 parts byweight of a ketone resin (Kunstharz AP), and 2 parts by weight ofAcridingelb G (Schultz, No. 901). After grinding and sieving, a yellowcolored toner is obtained which, when mixed with sodium chloridecrystals at a ratio of 2:1, forms a developer which yields reflex imagesof very good contrast, when used in the method of Example 1.Alternatively, an enlargement of a negative microfilm may be projectedonto the negatively charged electrophotographic paper by means of aprojector'and the latent enlarged image thus formed may be treatedwiththe developer powder. A

, positive enlargement is thus obtained. 1

For this purpose, the developer is contacted in known not struck bylight during exposure and which still have an electrostatic charge.Images are formed which correspond to the master used.

The developer of the present invention is preferably used for negativelycharged layers. During development, the toner adheres to those parts ofthe electrophotog'raphic reproduction material which were struck bylight, and a visible negative image of the original is obtained. oneadvantage of the developers according to the present invention, thatlittle or no marginal efiect appears at the contour lines, contrary tothe. developers hitherto used. Due to the mechanical stability thereof,the developers retain a distinctly negative charge even after long use.They are particularly suitable for producing enlargements frommicrofilms by the electrophotographic process.

The invention will be further illustrated by reference to the fololwingspecific examples:

Example 1 parts by weight of a zinc resinate (Erkazit-Harz RF) arefinely ground, mixed with one part by weight of Nigrosin spirit-soluble(Schultz Farbstoiftabellen, vol. 1, 7th edition, 1931, No. 985) and 0.5part by weight of copper-phthalocyanine and the mixture is melted. Aftercooling, the solidified melt is ground in a ball mill and sieved. Afraction, having an average grain size of 30- 50p, of the black-coloredtoner thus obtained is mixed in a ratio of 2:100 with glass balls havinga diameter of about 300 The developer thus obtained is suited for theproduction of reflex images. For this purpose an electro-photographicpaper, eg a zinc oxide paper or a metallic layer consisting e.g. ofaluminum provided with a zinc layer, is given a negative electric chargeof. 6000 volts by means of a corona discharge andthen exposed under anoriginal. The developer powder is then cascaded over the paper. Duringthis procedure, the finely distributed pigmented resin adheres to thoseparts of the layer which were struck by light during exposure, and anegative of the original becomes visible, which is subsequently fixed byslight heating. It shows good contrast eflect.

Example 2 The process described in Example 1 is repeated, with theexception that 50 parts byweight of magnesium resinate(Magnesium-Hartharz VII, 2), 2 parts by Weight of Fanalrot 6B (Schultz,No. 864-), and 2 parts by Weight of Sudan ll (Schultz, No. 532) areused. After grinding and sieving, a red toner is obtained which, whenmixed with glass balls at a ratio of 3:100, yields a It is 7 Example 4parts by weight of a manganese resinate (Manganresinat RMSS), 10 partslay-weight of montan wax, and 3 parts by weight of Alizarinblauschwarz B(Schultz, No. 1195) are treated as described in Example 1. Aftersieving, the toner is mixed-with tiny glass balls and yields a developerpowder which is suitable for the preparation of electrophotographicreflex images as described in Example 1.

Example 5 40 parts by weight of a cobalt resinate (Kobaltresinat A71)and 20 parts by Weight of colophony are melted, as described in Example1, with 2 parts by weight'of Pigmentschwarz' B (Schultz, No; 1361) and 1part by weight of Fanalblau B (Schultz, No. 822). After cooling, thesolidified mixture is ground and sieved. The toner thus obtained ismixed, at a ratio of 3: 100, with iron powder and then distributedbymeans of a bar magnet over a latent electrostatic'image produced'inaccordance with the method described in Example 1. The toner adheres tothose parts of the layer which were struck by lightduring exposure. Areverse imageof the original used is thus obtained, e.g. a positiveimage from a negative original.

Example 6 containing about 1 percent Co, 5 percent Pb, and 1 percentMn), 10 parts by weight of a zinc-calcium-resinate (Kunstharz 445) and 4parts by weight of Diamanatschwarz F, (Schultz, No. .614). The mixture,is ground, sieved, and then mixed, at aratio of 2:100, with tiny glassballs. A developer is thus obtained which is suited for the productionof electrophotographic reflex images. For this purpose a paper basecoated,'e.g. with an organic semi-conductor (e.g.2,5-bis-(4'-diethyl-amirio-phenyl- 1) 1,2,4 oxdiazole described inBelgian Patent No. 558,078)-is negatively charged and then exposed underan original. The developer powder is then cascaded over the paper,whereby the finely distributed colored resin adheres to those parts ofthelayer which were struck by light during exposure and a'negativeof theoriginal becomes visible. The image is fixed by treatment withtrichloroethylene vapors.

Example 7 30 parts by weight of iron resinate, 5 parts by weight ofcopper resinate, and 1 part by weight of Direkttiefschwarz E (Schultz,No. 671) are melted together and, after cooling, are ground and sieved.The toner, having a grain size of 50-100 is mixed with glass balls in aratio of 5:100. The developer thus obtained is suited for the productionof reflex images in accordance with the method described in Example 1.Instead of copper resinate, there may be used barium or iron resinate.

Example 8 50 parts by weight of a zinc resinate (Erkazit Zinkharz 165),parts by weight of an aluminum salt of a resinic acid (aluminum salt ofthe Albertol acid, Albertat 175), 10 parts by weight of l-naphthol, and2 parts by weight of Methylviolet B (Schultz, No. 783) are treated asdescribed in Example 1. After sieving, the toner is mixed at a ratio of3:100 with iron powder. The developer thus obtained is suited for theproduction of refiux images. For this purpose an electrophotographicpaper, e.g. zinc oxide paper, is given a negative electric charge of6000 volts by means of a corona discharge and then exposed under anoriginal. Subsequently, the developer is evenly distributed over thelatent electrostatic image by means of a bar magnet. The toner adheresto those parts of the layer which were struck by light during exposureso that a reverse image of the original used is obtained, e.g. apositive image of a negative original.

Example 9 50 parts by weight of a zinc resinate (Erkazit Zink RF) areground, mixed with 1 part by weight of Nigrosin spirit-soluble (Schultz,No. 985), and then melted. After cooling, the melt is ground in a ballmill and sieved. The black-colored toner, having a grain sizeof 3050,u.,is mixed with glass balls of about 300p. diameter at a ratio of 2:100.The developer thus obtained may be used for the production of directimages on layers having a positive charge. For this purpose, anelectrophotographic layer, e.g. an aluminum foil provided with aselenium layer, produced by means of selenium vapors, is given apositive electric charge of 6000 volts by means of a corona dischargeand then exposed under an original. Subsequently, the developer powderis cascaded over the foil. The finely distributed pigmented resinadheres to those parts of the layer which were not struck by lightduring exposure. An image corresponding to the original used becomesvisible which is fixed by heating; it shows very good contrast.

Example 10 The procedure described in Example 1 is repeated, using forthe melting process 50 parts by weight of a magnesium resinate, parts byweight of magnesiumphthalocyanine and 2 parts by weight of MethylengrunB (Schultz, No. 1040). After grinding and sieving, a green colored toneris obtained, which, when mixed with iron powder at a ratio of 3:100,yields a developer powder which may be cascaded over a latentelectrostatic image produced in accordance with the method described inExample 1. From a negative original a positive image is obtained.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. A dry developer for electrophotographic purposes, capable of beingnegatively charged, comprising a finelydivided inorganic carrier havingan average particle size in the range of about 100 to 600 and afinely-divided metal resinate toner having an average particle size inthe range of about 1 to about 100/J, the weight ratio of carrier totoner being in the range of about 100:30 to about 100:0.1.

2. A developer according to claim 1 including a pigment.

3. A developer according to claim 1 including a dyestuff.

4. A developer according to claim 1 in which the metal of the metalresinate is selected from the group consisting of aluminum, barium,lead, calcium, cerium, iron, cobalt, copper, magnesium, manganese, andzinc.

5. A device according to claim 1 including a resin having a low meltingpoint.

6. A developer according to claim 1 including a Wax.

7. A developer according to claim 1 including an aromatic organiccompound of low molecular weight.

8. A developer according to claim 1 in which the resinate is zincresinate.

9. A developer according to claim 1 in which the resinate is magnesiumresinate.

10. A developer according to claim 1 in which the resinate is calciumresinate.

11. A developer according to claim 1 in which the resinate is manganeseresinate.

12. A developer according to claim 1 in which the resinate is cobaltresinate.

13. A developer according to claim 1 in which the resinate iscobalt-lead-manganese resinate.

14. A developer according to claim 1 in which the resinate is copperresinate.

15. A dry process for developing an electrostatic image Which comprisescontacting the image with a negatively charged developer comprising afinely-divided inorganic carrier having an average particle size in therange of about to 600 2 and a finely-divided metal resinate toner havingan average particle size in the range of about 1 to about 100;/., theweight ratio of carrier to toner being in the range of about 100230 toabout 10020.1, and fixing the image.

16. A process according to claim 15 in which the developer includes apigment.

17. A process according to claim 15 in which the developer includes adyestuff.

18. A process according to claim 15 in which the metal of the metalresinate is selected from the group consisting of aluminum, barium,lead, calcium, cerium, iron, cobalt, copper, magnesium, manganese, andzinc.

19. A process according to claim 15 in which the developer includes aresin having a low melting point.

20. A process according to claim 15 in which the developer includes awax.

21. A process according to claim 15 in which the developer includes anaromatic organic compound of low molecular weight.

22. A process according to claim 15 in which the resinate is zincresinate.

23. A process according to claim 15 in which the resinate is magnesiumresinate.

24. A process according to claim 15 in which the resinate is calciumresinate.

25. A process according to claim 15 in which the resinate is manganeseresinate.

26. A process according to claim 15 in which the resinate is cobaltresinate.

27. A process according to claim 15 in which the resinate iscobalt-lead-manganese resinate.

28. A process according to claim 15 in which the resinate is copperresinate.

References Cited in the file of this patent UNITED STATES PATENTS2,019,981 Krauss Nov. 5, 1935 2,173,699 Siegel Sept. 19, 1939 2,463,044McLean Mar. 1, 1949 FOREIGN PATENTS 693,900 Great Britain July 8, 1953

1. A DRY DEVELOPER FOR ELECTROPHOTOGRAPHIC PURPOSES, CAPABLE OF BEINGNEGATIVELY CHARGED, COMPRISING A FINELYDIVIDED INORGANIC CARRIER HAVINGAN AVERAGE PARTICLE SIZE IN THE RANGE OF ABOUT 100 TO 600$ AND AFINELY-DIVIDED METAL RESINATE TONER HAVING AN AVERAGE PARTICLE SIZE INTHE RANGE OF ABOUT 1 TO ABOUT 100$, THE WEIGHT RATIO OF CARRIER TO TONERBEING IN THE RANGE OF ABOUT 100:30 TO ABOUT 100:0.1.
 15. A DRY PROCESSFOR DEVELOPING AN ELECTROSTATIC IMAGE WHICH COMPRISES CONTACTING THEIMAGE WITH A NEGATIVELY CHARGED DEVELOPER COMPRISING A FINELY-DIVIDEDINORGANIC CARRIER HAVING AN AVERAGE PARTICLE SIZE IN THE RANGE OF ABOUT100 TO 600$ AND A FINELY-DIVIDED METAL RESINATE TONER HAVING AN AVERAGEPARTICLE SIZE IN THE RANGE OF ABOUT 1 TO ABOUT 100$, THE WEIGHT RATIO OFCARRIER TO TONER BEING IN THE RANGE OF ABOUT 100:30 TO ABOUT 100:0.1,AND FIXING THE IMAGE.